This invention relates to an apparatus and method for positioning a printing mechanism, and more particularly to a printing mechanism for positioning a printing mechanism between printing and maintenance stations in a mail handling apparatus.
Mail handling machines, such as that described in U.S. Pat. No. 4,935,078 process mixed mailpieces (varying size) in a high speed manner. These known mail handling machines typically include a front end feeder, a singulator, a moistener, a sealer, and a printing device. The front end feeder shingles the incoming mailpieces (such as envelopes) and the singulator grabs the bottom envelope from the shingled stack of envelopes for subsequent processing downstream. Upon passing by the singulator, the envelope is successively fed past the moistener where its flap portion is moistened and is then passed through a sealer where the flap is sealed prior to the printing of, for example, postage values thereon by the printing device (postage meter). Moreover, the mail handling machine may further include a scale for weighing the mailpieces and a tape mechanism for printing of indicia on a tape.
Modern mail handling machines utilize digital printing techniques for producing images on a mailpiece being processed therethrough. Conventional digital printing techniques include bubble jet, piezoelectric ink jet, and thermal ink transfer which each produce an image in a dot matrix pattern. That is, in digital ink jet printing individual printhead elements (such as resistors or piezoelectric elements) are selectively electronically stimulated to expel drops of ink from a reservoir onto a substrate. In the case of thermal ink transfer, individual resistive elements which contact a thermal inking transfer tape are selectively energized to transfer ink from the tape on to a substrate in contact with the tape. In either case, by controlling the energizing timing of the individual printhead elements in conjunction with the relative movement between the printhead and the mailpiece, a dot matrix pattern is produced in the visual form of the desired indicia.
Digital printing technology has significant advantages when used in a mail handling apparatus as compared to older technology which utilized either a flat platen or a rotary drum to imprint indicia on mailpieces. For example, if the variable indicia image data needs to be changed, it can easily be done through the installation of new or upgraded software versus having to replace the entire meter since the flat platen and drum do no get removed. Moreover, greater printing speeds can be obtained as compared to conventional mechanical printing systems. However, the use of a digital printhead in a mail handling apparatus presents special maintenance requirements which must be undertaken in order to ensure that the printhead continues to perform satisfactorily. That is, since the size of the nozzle openings in the printhead through which the individual drops of ink are expelled are very small, they can easily become clogged by debris or dried ink. If this occurs, the clogged nozzle will not be able to have ink expelled therethrough. Eventually, if enough nozzles become clogged, the indicia image produced will degrade to an unacceptable level. Accordingly, it is very important to keep the printhead nozzles free of any contamination when the printhead is not printing.
Typically, office apparatus having digital printheads have a maintenance station located at one end of the direction of travel of the printhead. The maintenance station includes a printhead cover which is designed to cover and hermetically seal the printhead nozzles as the printhead moves into a maintenance (home) position. The hermetic seal helps to prevent the ink from drying in the nozzles and provides a shield from contamination while not printing. Moreover, the maintenance station typically has wipers associated therewith which wipe the nozzles just prior to or after their being covered by the printhead cover. The wipers remove any contamination that may have been deposited on the nozzles during printing or ink accumulated during maintenance. Additional maintenance features which may be associated with the maintenance station include the ability to provide a vacuum burst to the nozzles to unclog clogged nozzles and a purge capability for clearing the nozzles.
As previously mentioned, conventional office apparatus typically move their printheads back and forth along a single path of travel. The maintenance station is often located at the one end of the path of travel in the home position such that after a printing operation the printhead returns to the home position where it is serviced by the maintenance station. However, in a mail handling apparatus the front end feeder, singulator, moistener, sealer, printing station, and stacker are typically aligned one after the other in the direction of travel of the mailpiece through the mail handling apparatus. This creates a mail handling apparatus with a long footprint. Accordingly, if a maintenance station for a digital printhead is placed in line with the flow of mail, it will add to the overall length of the machine. Additionally, since the maintenance station is situated within the mail flow, it is very vulnerable to collecting paper dust associated with the mailpieces. Thus, the printhead cover could collect paper dust therein which, in turn, could clog the printhead nozzles when the printhead is protected by the cover.